The only real surprise from the FDA's approval of Seattle Genetics' (Nasdaq: SGEN) Adcetris on Friday was the timing. After a unanimous recommendation from the FDA advisory panel, approval of the lymphoma treatment looked like a slam dunk on or around its PDUFA date of Aug. 30.

A decision 11 days before the FDA's goal is a little unexpected, but the agency seems to be handing down decisions quickly this month. Roche gained early approval for its melanoma drug Zelboraf. And Adventrx Pharmaceuticals (AMEX: ANX) heard back from the FDA earlier than expected, albeit not the decision shareholders were hoping for.

But investors in companies with upcoming FDA decisions -- Shire's (Nasdaq: SHPGY) Firazyr and Nupathe's Zelrix, for instance -- shouldn't necessarily expect the same treatment. Adcetris, Zelboraf, and Adventrx's Exelbine are all cancer drugs, so all we can say is that the reviewers in the Office of Oncology Drug Products are running ahead of schedule. In fact, Regeneron Pharmaceuticals (Nasdaq: REGN) announced last week that it will take three months longer to get an FDA decision about its macular degeneration drug, Eylea.

For Seattle Genetics, the first approval is a huge milestone. The biotech has funded some of its operations by licensing its antibody-drug conjugate technology to other drugmakers, but Adcetris will provide the first real revenue stream for the company. The types of lymphoma the drug treats are relatively rare, but Seattle Genetics can make up for the low volume with a high price tag. Adcetris will cost around $108,000 per patient -- assuming eight doses at $13,500 each -- and could theoretically be higher if patients take more doses.

Equally important, the approval is an endorsement of the ADC technology. Seattle Genetics has three more ADC molecules in the clinic -- all phase 1 -- in addition to 11 ADC partnerships from which it'll get royalties and milestones if the collaborators' drugs work.

I called Seattle Genetics a little overpriced in July, but since then it's fallen considerably and the risk of an FDA rejection -- however slight it was -- is gone, making the drugmaker considerably more appealing at this level.

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Fool contributor Brian Orelli holds no position in any company mentioned. Click here to see his holdings and a short bio. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.